“There's no doubt in my mind ... he was tortured not so much the way—pulling fingernails out with tools but by repeated drugging—sodium pentothal,” the retired Army general told the FOX Business Network’s Maria Bartiromo, adding that the drug’s frequent use is what led to Warmbier’s brain damage.

"Essentially it was the use of these drugs over and over again which caused the brain damage," he said.

Shaffer said North Korea was likely trying to figure out if he was a CIA spy.

“I think that during his confinement they did it over and over and I think that was one of the reasons that they released him,” he said. “But no doubt they kind of like saw that some things are going to go tragically wrong, we better get this guy out of here anyway so it served their purpose to get him out.”

Shaffer said the U.S. should not “sit back” and let a dictator like Kim Jong Un murder an American and “think they can get away with it.”

“We need to rethink our foreign policy,” he said, “in a way that those bad guys … understand that there’s going to be consequences for bad behavior."

President Trump slammed Otto's treatment by North Korea as a "disgrace" and said his administration will "be able to handle it."